A watchnight service (also called Watchnight Mass) is a late-night Christian church service. In many different Christian traditions, such as those of Moravians, Baptists, Methodists, Anglicans and Pentecostals, watchnight services are held late on New Year's Eve. This provides the opportunity for Christians to review the year that has passed and make confession, and then prepare for the year ahead by praying and resolving. The services often include singing, praying, exhorting, and preaching.

Watchnight service has added significance and history in the African-American community in the United States, since many slaves were said to have gathered in churches on New Year's Eve, in 1862, to await news and confirmation of the enactment of the Emancipation Proclamation by President Abraham Lincoln, on January 1, 1863.